Method of drilling wells



. actual drilling. In the latter case the shale may.

Patented July 1 1, 1939 UNITED STATES ma'rnon or DRILLING WELLS William V. Vietti and Allen D. Garrison, Houston, Tex., assignors to The Texas Company, New York, N. Y., v a corporation of Delaware No Drawing.

Application August 6, 1936,

Serial No, 94,586

21 Claims.

This invention relates to the drilling of wells and more particularly to the control of the heaving shale encountered in-the drilling of such wells.

More specifically, our invention relates to the preparation and use of drilling muds so constituted and controlled in composition that when employed in the drilling of a well traversing or penetrating a heaving shale formation, the heaving of the shale is substantially prevented. According. to our invention this may be accomplished by the use of a mixture of sodium siii-f cate with certain water-soluble salts in the drilling mud.

Drilling muds are almost universally used in the drilling of wells employed for tapping underground collections of oil, gas, brines and water. These muds fulfillvarious functions, the most important of which are to assist in the removal of cuttings from the wells,'to seal formations of gas, oil and water whichmay be encountered at various levels and to lubricate the drilling tools and the drill pipes which carry the tools.

In the course of drilling-wells the bores may encounter certain geological formations which are termed heaving shale. formations" or, more simply, heaving shale".- The term denotes -shale strata which do not remain'consolidated during the drilling operations. In some cases the shale heaves or caves into the hole when the drilling tools are removed therefrom and in other cases theshale may heave in the course of the hind or pinch the drill stem, thereby preventing its rotation or 'even resulting in its destruction.

Our experience leads us to conclude that there are various types of heaving shales which react differently; some may be controlled merely by mechanical methods, whereas others require chemical treatment for successful control.

ing the heaving of shales which may be controlled by mechanical means. One is that the heaving of shale is causedby pockets of high pressure gases which exist in the crevices and partings of shale formations. Another theory is thatthis class of heaving shales is undericonsiderable unrelieved stress and that the drilling of-a hole through the shale forms an opening into which the shale can slide or cave to partially relieve the inner stress. i

. 'I'he heaving shales which require chem-i treatment for successful control apparently disintegrate'when they are contacted'with aqueous drilling mud and experiments indicate that it is Var ious theories have been advanced for explain-y the water content of the drilling mud which brings about this disintegration. Several methods have been proposed for chemically controlling shales of this type, for example, one method involves incorporating in the drilling mud water 5 soluble salts such as calcium chloride, magnesium chloride or other salts. This method of treatment is based upon the theory that the heaving or disintegration of the shale is brought about by the osmosis of the. water from the drilling 10 fluid in the well bore to the more concentrated salt solution within the shale pores, the pressure subsequently developed within the shale beingsufllciently great to disintegrate it.

We have found that the incorporation of salts 15 having a high osmotic pressure in drilling muds does not prevent the heaving of shale contacted with such drilling muds. We have also found that heaving shales which disintegrate with great rapidity in water also disintegrate in aque- 20 ous solutions of alkali metal and alkaline earth salts. 0n the basis of this work we have concluded that osmosis is not responsible for the heaving of shale.

We have previously disclosed in co-pending ap- 25 plication Serial No. 91,702, filed July 21, 1936, that, by incorporating relatively large quantities of certain sodium silicates in drilling muds, it is possible, by the use of such muds, to penetrate heaving shales successfully. According to our 30.

present invention, we have discovered that, by using certain types ofwater-solublia salts in combinationwith sodium silicate in drilling muds, substantial improvements may be obtained. These improvements consist, principally, of a 35 more complete protection of the heaving shale, and a substantial reduction in the quantity of sodium silicate required in the drilling mud. We -have found that sodium silicates, in which the ratiov of silica to sodium oxide is greater than 1, 4 and preferably, sodium silicates'in which the ratio of silica to sodium oxide is greater than 1.5

to 1.0, may be employed. We contemplate the use of any of the sodium silicates up to and including sodium silicates having a ratio of silica 45 to sodium oxide of 3.9 to 1.0.

. Commercial sodium silicates are commonly. available in water solutions of varying viscosity. They are placed on the market in water solution at concentrations near the practical limit of viscosity tor the purpose of avoiding the expense of s pping unnecessary amounts of water. It is ing molecular ratios of silica to sodium. oxide of from 1.5:1 up to 3.9:1. We appreciate that commercial sodium silicate solutions are prepared by dissolving in water sodium silicates which are sometimes spoken of in the art as sodium silicate glass". In the practice of our invention, we contemplate the use of commercial sodium silicate solutions without regard to their method of preparation. In the use of the terms "sodium silicate" throughout the specification and claims, we refer to the commercially available sodium silicate solutions mentioned above.

In the selection of salts for use in combination with these sodium silicates, we employ one or more sodium or potassium salts of the following negative ions, said ions being listed in decreasing order of activity: thiocyanate, chlorate, iodide, nitrate, bromide, chromate, and chloride. The relative amounts of both the sodium silicate and the salt or salts employed will be more fully described hereinafter. I

The method of this invention is in no wise similar to those methods of consolidating rock,

formations, which involve treating the rock formations with sodium silicate or other salts to react with water-soluble precipitants such as polyvalent metal salts or acids, whereby waterinsoluble precipitates are formed. On the contrary, the success of our process is not dependent upon the precipitation of water-insoluble silicates by reaction of the sodium silicate content of our mud with water-soluble precipitating salts or acids contained within the pores of the heaving shale. Furthermore, the success of our invention is not due to the precipitation, of silica or silicates from the sodium silicate content of our drilling muds by those salts which we incorporate in the drilling muds since we avoid the use of concentrations of sodium silicate and water-soluble salts, which would yield any substan'i tial precipitation of silica or silicates.

We have found that the improvement resulting from the use of a salt in combination with the sodium silicate is not a function of the osmotic pressure of the salt solution. In support of this, our experiments have demonstrated that lithium chloride, among other materials, may not be substituted in equimolecular quantities, for the salts which we have disclosed, although its osmotic pressure is substantially the same. Furthermore, we have additional evidence, which is disclosed subsequently, which indicates that the protection of heaving shales is not a function of osmotic pressures of the salt solutions employed.

We realize that the use of sodium silicate in small amounts in drilling muds has been proposed for maintaining drilling muds in the proper state of colloidal dispersion. In these cases, sodium silicate is employed to bring about the precipitation of calcium and'magnwium ions which apparently have been recognized as having a deleterious efiecton drilling muds. In using sodium silicate for this purpose, only suillcient is used cation of our invention. This research work has indicated that some salts, when used in combination with sodium silicates, do not improve the drilling mud, 'and such protection as is obtained is due solely to the sodium silicate. Furthermor we have found that some salts are even do ental, and that they reduce the protection which the sodium silicate alone mightaiford.

Our researches indicate that both the positive and negative ion constituents of the salts used must be selected from certain speciflc groups. Our investigations have shown, in so far as the positive ions are concerned, that the alkali metals sodium and potassium, when combined with the proper hegative ions, have a beneficial eifect. Of these two we have found that the potassium ions are somewhat more effective in the practice of our invention but we also contemplate the use of sodium ions or mixtures of the two. Our researches have revealed the fact that all negative ions, when combined with sodium or potassium, are not equally effective in improving the protective action of sodium silicate. In fact we have discovered that the ions may be placed in a series substantially expressing the relative protection afforded by equivalent quantities of the sodium or potassium salts when incorporated in drilling fluids containing the same quantities of sodium silicate. If the salt is chosen from the less eifective members of the series, we have that these salts do not function by virtue of their osmotic pressure.

Our invention maybe applied in numerous ways,

for example, a preferred type of sodium silicate may be added to a previously prepared drilling mud and the salt added thereto; or else, a drilling mud may be formed by incorporating clay or other finely-divided materials in a solution of sodium silicate and the salt dissolved therein; or

else, a saturated solution. of the salt in water may be prepared, mixed with the calculated amount of sodium silicate and suspended matter such as finely-divided solids of the type of clay or mixtures of clay with iron oxide, barytes, and the like added thereto. Wedo not intend to limit ourselves to any particular method of compounding or preparing the drilling muds employedby us in effecting the operation of our invention.

In the general practice of our invention, we propose to use a drilling fluid containing not less than 20% by volume of one of the previously described sodium silicates or mixtures thereof, and not less than 2% (by weight of the aqueous medium of the drilling mud) of at least one of the salts which we have disclosed.

As typical examples of the application or our invention, we give herewith descriptions of several drilling muds which we have employedfor successfully drilling through strata of heaving shales located on the Bryan Mound at Freepcst, Texas.

Example 1 A drilling fluid comprising suspended clay, water, about 27% by volume of a sodium silicate in which the molecular ratio of silica to sodium oxide was 3.22 to 1 and in which the watercouproximately 11.7 lbs, per gallon and had a viscosity of 25 seconds (500 cc. through the Marsh H tent was 62%, and sodium chloride in the concentration 2.25%by weight of the aqueous medium, exclusive of suspended solids. This drilling fluid weighed 10.2 lbs. per gallon and had a viscosity 01.;24 seconds (500 cc. through the'Marsh funnel viscosimeter).

Example 2 v A drilling fluid comprising suspended clay and barytes," water, about 34% by volume of sodium silicate in which the molecularratio of silica to sodium oxide was 2 to 1 and in which the water content was 56%, and potassium chloride in the concentration 7.7% by weight of the aqueous medium, exclusive ofthe suspended solids. This drilling fluid weighed 11.9 lbs. per gallon and had a viscosity of 29 seconds (500 cc. through the March tunnel viscosiineter).

Example 3 A drilling fluid comprising suspended clay and barytes,'water, about 51% by volume of sodium silicate in which the molecular ratio of silica to sodium oxide was 2 to 1 and in which the water content was 56% potassium chloride in 4 the amount of about 5% by weight of the aqueous medium, exclusive of suspended solids and sodium chloride in the amount of about 10.7% by weight of the aqueous medium, exclusive of suspended solids. This drilling fluid weighed approximately 12.7 lbs. per gallon and had a viscosity of 32 seconds (500. cc. through the March tunnel viscosimeter) Example 4 A drilling fluid comprising suspended clay and 'barytes, water, about 36% by volume of sodium silicate in which the molecular ratio of silica to sodium oxide was 2 to 1 and in which the water .content was 56%,' potassium chloride in the amount of about 4.9% by weight of the aqueous medium, exclusive of Suspended solids and sodium chloride in-thefamount of about 1.5% by weight of the aqueous medium,.exclusive of suspended solids. This drilling fluid weighed apfunnel viscosimeter) Example 5 A drilling fluid comprising suspended clay and barytes, water, about 51% by volume of sodium silicate in which the molecular ratio of silica to sodiumoxide was 2 to 1 and in which the water content was 56%, potassium chloride in the amount of about 5.2% by weight of the aqueous medium, exclusive of suspended solids and sodium, chloride in the amount of about 3.1% by weight of the aqueous medium, exclusive of suspended solids. This drilling fluid weighed about -l2.4 lbs. per gallon and had a viscosity of seconds (500 cc. through the Marsh funnel viscosimeter).

Theabove drilling muds were used in the actinously circulated through the drill pipe to the locu'sjof drilling where it picked up cuttings and drilling debris and carried them suspended therein upwardly to the surface where the cuttingszq laden mud waspassed into the settling pit and 15 thereof as was evidenced by the fact that no ap-.

cepted manner, the drilling mud used being conpreciableincrease in the amount of suspended finely-divided solids in the muds was observed.

Although we employed 27% by volume of sodium silicate in Example 1, 34% by volume in Example 2, 51% by volume in Example 3, 36% by volume in Example 4, and 51% by volume in Example 5, we contemplate the use of both lower and higher amounts, preferably in the amount of not less than 20% by volume. Although we have used sodium silicate in which the molecular ratio of silica to sodium oxide is 3.22 to l in Example 1, and 2 to 1 in Examples 2, 3, 4, and 5, we contemplate the use of sodium silicates of other molecular ratios and prefer to employ those sodium silicates having molecular ratios of silica to sodium oxide in the range 1.5 to 1 up to 3.9 to 1.

We recognize that sodium silicate is also available in ratios of silica to sodium oxide ranging from 1521.0 down to 1.0:1.0 (sodium metasilicate), and that these sodium silicates partake of the properties of the sodium silicates of 1.5 to 1 ratio in varying degrees. Some of these sodium silicates may be effective in practicing our invention when encountering certain shales, but for general use, we prefer to use sodium silicates within the range of ratios of silica to sodium oxide of 3.9 to 1.0 to 1.5 to 1.0.

We are aware of the fact that certain sodium silicates are unstable in the presence of concentrated salt solutions. This instability becomes more marked as the ratio of silica to sodium it has been found desirable to use sodium silicates having the lower molecular ratios of silica to sodium oxide in order to prevent salting out of sodium silicate or silica gel.

It is desirable,'therefore, to correlate the character of sodium silicate solutions employed with the concentration of sodium or potassium salts. In this manner it is possible to avoid exceeding the saturation point of any of the dissolved components, i. e., sodium silicate and the sodium and potassium salts referred to above.

Obviously many modifications and variations of the invention as hereinbefore set'for th may be made without departing from the spirit and scope thereof and only such limitations should be imposed 'as are indicated in the appended claims.

We claim:

1. A drilling mud useful for preventing the heaving of shale comprising an aqueous suspension of a finely divided solid, said aqueous suspension having dissolved therein not less than 20% by volume of a sodium silicate in which the molecular ratio of silica to sodium oxide falls within the rangeof from 3.9:1 to 15:1, and at least one salt selected from the group consisting" of the sodium and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersion falling within the range of from 2% by weight of the aqueous medium up to the saturation valuepension having dissolved therein not less than 20% by volume of a sodium silicate in which the molecular ratio of silica to sodium oxide falls within the range of from 3.9:1 to 15:1, and at least one salt selected from the group consisting of the sodium and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersion falling within the range of from 2% by weight of the aqueous medium up to the concentration at which an appreciable precipitation of sodium silicate and silica gel occurs. i

3. A drilling mud usei'nl for preventing the heaving of shale comprising anaqueous suspension of clay, having dissolved therein about 27% by volume of sodium silicate in which the'molecular ratio of silica to sodium oxide is about 3.2 to 1, and about 2% by weight the aqueous medium of sodium chloride.

4. A drilling mud useful for preventing the heaving of shale comprising an aqueous suspension of clay, having dissolved therein about 34% by volume of sodium silicate in which the molecular ratio of silica to sodium oxide is about 2 to.

1 and about, 7.7% by weight of the aqueous medium of potassium chloride.

5. A drilling mud useful for preventing the heaving of shale comprising an aqueous suspension of finely divided solids having dissolved therein about 51% by volume of sodium sflicate in which the molecular ratio 01' silica to sodium oxide is 2 to 1, potassium chloride in the amount of about 5% by weight of the aqueous-medium and sodium chloride in the amount of about 10.7% by weight of the aqueous medium.

6, A drilling mud useful for preventing the heaving of shale comprising an aqueous suspension of finely divided solids having dissolved therein about 36% by'volume of sodium silicate in which the molecular ratio of silica to sodium oxide is 2to 1, potassium chloride in the amount a. In "the drilling of wells with the use or a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising an aqueous suspension of a finely divided solid, said aqueous suspension having dissolved therein not less than 20% by volume of a sodium silicate in which the molecular ratio of silica to sodium oxide falls within the range of from 3.9:1' to 1.5:1, and at least one salt selected from the group consisting of the sodium and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content oi the dispersion falling within the range of from 2% by weight of the aqueous medium up to the saturation value of a dissolved component.

9. In the drilling of wells with the use of a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising an aqueous suspension of a finely divided solid, said aqueous suspension. having dissolved therein not less than 20% by volume of a sodium silicate in which the molecular ratio of silica to sodium oxide falls within the range of from 3.9:1 to 1.5:1, and at least one salt 'selected from the group consisflna? oi the sodium hates, chlorates,

' arouses and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersion falling within the range of from 2% by weight of the aqueous medium up to the concentration at which an appreciable precipitation of sodium silicate and silica gel occurs.

10. In the drilling of wells with the use of a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising an aqueous suspension of clay, having dissolved therein about 27% by volume of sodium silicate in which the molecular ratio oi silicate to sodium oxide is about 3.2 to 1, and about 2% by weight of the aqueous medium of sodium chloride.

11. In the drilling of wells with the use oi a drilling mud, the method oi. preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising an aqueous suspension oi clay, having dissolved therein about 34% by volume of sodium silicate in which the molecular ratio of silica to sodium oxide is about 2 to 1 and about 7.7% by weight or the aqueous medium at potassium chloride.

12. In the drilling of wells with the use of a drilling mud, the method for preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising an aqueous suspension of finely divided solids having dissolved therein about 51% by volume of sodium silicate in which the molecular ratio of silica to sodium oxide is 2 to 1, potassium chloride in the amount of about 5% by weight of the aqueous medium and sodium chloride in the amount of about 10.7% by weight of the aqueous medium.

13. In the drilling of wells with the use of a drilling mud, the method oi preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising an aqueous suspension or finely divided solids having dissolved therein about 36% by volume of sodium silicate. in which the molecular ratio of silica to -sodium oxide is 2 to 1, potassium chloride in the amount or about 4.9% by weight of the aqueous medium and sodium chloride in the amount or about 1.5% by weight of the aqueous medium.

14. In the drilling of wells with the use 0! a drilling mud, the method of preventing the heaving of shale encountered in the well, which comprises circulating through the well a drilling mud comprising an aqueous suspension of finely divided solids having dissolved therein about 51% by volume of sodium silicate in which the molecular ratio of silica to sodium oxide is 2 to 1, potassium chloride in the amount of about 5.2% by weight of the aqueous medium and sodium chloride in the amount of about 3.1% by weight ofaqueous medium.

15. A drilling mud useful for preventing the heaving of shale comprising an aqueous suspension of a finely divided solid, said aqueous suspension havlng dissolved therein not .less than by volume oi a sodium silicate in which the molecular ratio of silica to sodium oxide falls within the range of from 3.0:1 to about 1.1:1.0 and at least one salt selected from the group consisting of the sodium and potassium thiocyaiodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersionialling within the range of from 2% by weight of the aqueous medium up to the saturation value of a dissolved component.

16. A drilling mud useful for preventing the heaving of shale comprising an aqueous suspension of a finely divided solid, saidaqueous suspension having dissolved therein not less than 20% by volume .of a sodium silicate in which the molecular ratio of silica to sodium oxide falls within the range of from 3.9:1 to about l.1:1.0,- and at least one salt selected from the group consisting of the sodium and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersion falling within the range of from 2% by weight of the aqueous medium up to. the

concentration at which an appreciable precipi tation of sodium silicate and silica gel occurs. 17. A drilling mud comprising water glass and an alkali metal salt of a strong mineral acid, the

salt and water glass each being present in substantial proportion and in combined amount adapted to prevent the heaving of shale.

18. A drilling mud comprising water glass and one or more salts selected from the group consisting of sodium and potassium salts of strong mineral acids, the salt and water glass each being present in substantial proportion and in combined amount adapted to prevent the heaving of shale.

19. A drilling mud comprising water glass and an alkali metal chloride, the chloride and water glass each being present in substantial proportion and in combined ount adapted to prevent the heaving of shal 20. A drilling mud comprising water glass and 'at least one salt selected from the group consisting of sodium and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt and water glass each being present in substantial proportion and in combined amount adapted to prevent the heaving of shale.

21. In the drilling of wells with the use of a drilling mud, themethod which comprises circulating through the well a mud constituted according to claim 1'7. 

